body{
  background-color: #f1f1f1;
}

.chat-header{
  width: 100%;
  height: 70px;
  line-height: 70px;
  background-color: #fff;
}

.nav{
  width: 1200px;
  margin: 0 auto;
}

.nav a{
  float: left;
  padding: 0 30px;    
  font-size: 16px;
  color: #333;
  border-top: 4px solid transparent;
}

.nav a.on{
  border-top: 4px solid #109d59;
  color: #109d59;
}